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        console.log(Math.E);
        //向上取整
        console.log(Math.ceil(1.00001));//2
        //向下取整
        console.log(Math.floor(1.99999999));//1
        //四舍五入
        console.log(Math.round(1.45))//1
        console.log(Math.round(1.5001))//2
        console.log(+new Date());
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